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Method for fabricating a locally passivated germanium-on-insulator substrate
8372733 Method for fabricating a locally passivated germanium-on-insulator substrate
Patent Drawings:Drawing: 8372733-2    Drawing: 8372733-3    Drawing: 8372733-4    Drawing: 8372733-5    Drawing: 8372733-6    
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Inventor: Signamarcheix, et al.
Date Issued: February 12, 2013
Application:
Filed:
Inventors:
Assignee:
Primary Examiner: Hu; Shouxiang
Assistant Examiner:
Attorney Or Agent: Winston & Strawn LLP
U.S. Class: 438/480; 257/E21.568; 438/165; 438/458; 438/479
Field Of Search: 438/165; 438/406; 438/407; 438/458; 438/479; 438/480; 257/347; 257/E21.568
International Class: H01L 21/20; H01L 21/00; H01L 21/36; H01L 21/30
U.S Patent Documents:
Foreign Patent Documents: 1 081 748; 1 659 623; 2 876 220; 2006-148066; 2008-516443; WO 2007/148072
Other References: Signamarcheix, T. et al., "Germanium Oxynitride (GeO.sub.XN.sub.Y) as a Back Interface Passivation Layer for Germanium-on-InsulatorSubstrates", Applied Physics Letters, vol. 93, pp. 022109-1-022109-3, (2008). cited by applicant.
Sugawara et al., "Physical and electrical properties of plasma nitrided germanium oxynitride," J. Vac. Sci. Technol. B, 24(5):2449-2456 (2006). cited by applicant.
European Search Report, Application No. EP 08290827, Dec. 16, 2008. cited by applicant.









Abstract: The invention relates to a method for fabricating a locally passivated germanium-on-insulator substrate wherein, in order to achieve good electron mobility, nitridized regions are provided at localised positions. Nitridizing is achieved using a plasma treatment. The resulting substrates also form part of the invention.
Claim: What is claimed is:

1. A method of for fabricating a locally passivated germanium-on-insulator substrate which comprises the steps of: providing a substrate having at least a germanium (Ge)containing surface layer as a source substrate, providing passivated local regions made of germanium oxynitride (GeON) along with non-passivated local regions in or on the surface layer for use in forming the germanium-on-insulator substrate, providing apredetermined splitting area in the source substrate, bonding the source substrate to a handle substrate by means of an insulator layer intervening between the source and handle substrates, with the insulator layer in contact with both the passivated andnon-passivated local regions, and detaching the source substrate at the predetermined splitting area to thereby obtain the locally passivated germanium-on-insulator substrate.

2. The method of claim 1, wherein the surface layer of the source substrate is a silicon germanium layer or an epitaxial Ge layer.

3. The method of claim 1, wherein the providing of the passivated regions includes providing a patterned mask over the source substrate and nitridizing the source substrate with a plasma.

4. The method of claim 3, wherein the plasma is a NH.sub.3, N.sub.2 or N.sub.2O plasma and which further comprises applying an oxygen or argon plasma before applying the NH.sub.3, N.sub.2 or N.sub.2O plasma.

5. The method of claim 3, wherein the mask is a shadow mask that includes Teflon or metal, or a deposited mask that includes a photoresist or germanium oxide.

6. The method of claim 3, which further comprises providing the mask by providing a germanium oxide layer on the source substrate, providing a photo resist layer on the germanium oxide layer, nano-imprinting the photo resist layer, andproviding the pattern by plasma or reactive ion etching.

7. The method of claim 1, which further comprising annealing the locally passivated regions for 1 hour or more at about 600.degree. C.

8. The method of claim 1, which further comprises activating the source substrate or the handle substrate, or both, using a plasma treatment that includes an oxygen plasma or a NH.sub.3, N.sub.2 or N.sub.2O plasma prior to bonding, and thenbonding the substrates directly after the plasma treatment without any intervening further process step.

9. The method of claim 1, which further comprises providing the insulator layer comprising a dielectric on the source substrate or on the handle substrate, or on both substrates prior to bonding, wherein the dielectric layers comprise an oxide.

10. The method of claim 1, which further comprises a step of providing alignment marks on or in the source substrate configured and arranged to identify the positions of the locally passivated regions.

11. The method of claim 10, wherein the step of providing alignment marks comprises a step of providing a pattern of recesses in the source substrate pattern, with the recesses optional including a dielectric layer therein.

12. The method of claim 11, which further comprises providing the predetermined splitting area such that it crosses the recesses in the source substrate.

13. The method of claim 1, wherein the passivated local regions have micrometric or nanometric sizes.

14. A method for fabricating a locally passivated germanium-on-insulator substrate which comprises the steps of: providing a substrate having at least a germanium (Ge) containing surface layer as a source substrate, subjecting the sourcesubstrate surface layer to reactive ion etching to provide recesses therein, providing passivated local regions made of germanium oxynitride (GeON) in or on the surface layer by providing a patterned mask over the Ge containing surface layer andrecesses, with regions on the surface layer blocked by the mask not being passivated, providing a predetermined splitting area in the source substrate, bonding the source substrate to a handle substrate by means of an insulator layer intervening betweenthe source and handle substrates and in contact with the passivated local regions and the non-passivated local regions, and detaching the source substrate at the predetermined splitting area to thereby obtain the locally passivated germanium-on-insulatorsubstrate.

15. The method of claim 14 which further comprises providing alignment marks configured and arranged to identify the positions of the locally passivated regions.

16. The method of claim 14 which further comprises providing an electronic device comprising nmos and pmos device structures on or in the germanium-on-insulator substrate, wherein the nmos structures are provided over the localised, passivatedregions, and the pmos structures are provided over other regions of the germanium-on-insulator substrate.

17. The method of claim 14 which further comprises providing alignment marks configured and arranged to identify the positions of the locally passivated regions.

18. The method of claim 14 which further comprises providing an electronic device comprising nmos and pmos device structures on or in the germanium-on-insulator substrate, wherein the nmos structures are provided over the localised, passivatedregions, and the pmos structures are provided over other regions of the germanium-on-insulator substrate.
Description: BACKGROUND

The invention relates to a method for fabricating a germanium-on-insulator (GeOI) substrate and a germanium-on-insulator substrate.

Germanium-on-insulator structures are generally known in the art. EP 1 659 623 A1 discloses a method to fabricate a germanium-on-insulator (GeOI) substrate during which a germanium oxynitride (GeO.sub.xN.sub.y) layer is provided as a burieddielectric between a Ge layer and a handle substrate, e.g., a Si wafer. T. Signamarcheix et al in Applied Physics Letters 93, 022109 (2008) describes the advantageous effect of the presence of a GeO.sub.xN.sub.y layer underlying the active Ge layerconcerning the electron mobility. Thus, this kind of substrate can advantageously be used for electronic devices based on n-MOS technology. It appears, however, that the hole mobility became affected by the presence of the GeO.sub.xN.sub.y layer sothat concerning p-MOS devices, this kind of substrate is less suited.

Accordingly, there is a need for improved germanium-on-insulator substrates and these are now provided by the present invention.

SUMMARY OF THE INVENTION

The invention relates to a method for fabricating a locally passivated germanium-on-insulator substrate which comprises the steps of: providing a germanium (Ge) substrate or a substrate comprising a Ge containing layer, in particular anepitaxial Ge layer or a silicon germanium layer (SiGe), as a source substrate, and locally treating the source substrate to provide passivated regions, in particular regions of GeO.sub.xN.sub.y. With the inventive method, a germanium-on-insulatorsubstrate with satisfying electronic properties, in particular high electron mobility in the passivated zones and hole mobility in the non passivated regions, can be obtained. In case of a SiGe layer, the inventive method is particularly advantageousfor high Ge contents of more than 50%, in particular more than 70%.

Preferably, the passivation of the source substrate, the surface of which comprises a native Ge oxide which needs to be stabilized, is achieved by providing a germanium oxynitride (GeO.sub.xN.sub.y) layer with a substantial nitrogen content of20 to 50%. With this GeO.sub.xN.sub.y layer, the desired passivation and the desired improvements concerning electron mobility in the Ge layer directly above the passivated region in the final substrate, can be achieved.

Advantageously, the source substrate can be locally treated by providing a patterned mask over the source substrate. With this method, any pattern can be realised on the source substrate so that the regions which should show a high electronmobility according to the desired final structures, can be achieved. As an alternative, maskless patterning methods can also be used.

Preferably, the passivating can be achieved by nitridizing. Using this method, advantage is taken of the already present natural Ge oxide to obtain the GeO.sub.xN.sub.y layer.

Preferably, the source substrate can be locally treated using a plasma, in particular a NH.sub.3, N.sub.2 or N.sub.2O plasma. According to a variant, the NH.sub.3, N.sub.2 or N.sub.2O plasma can be diluted in 10% to 30% Ar. With this methodand in particular at low pressure, in particular with a plasma of less than 40 mTorr, preferably in a range of 1 to 10 mTorr, a significant amount of up to 40% Nitrogen atoms can be incorporated into the substrate. Optimized results have been achievedfor a pressure of 5 mTorr. This process is preferably carried out at a temperature of 25.degree. C. up to 600.degree. C.

Advantageously, the local treatment of source substrate can further comprise applying an oxygen and/or argon plasma, in particular before applying the NH.sub.3, N.sub.2 or N.sub.2O plasma. The oxygen comprising plasma can advantageously be usedto improve and/or thicken the germanium oxide layer on top of the source substrate. Providing the nitrogen containing plasma after the oxygen plasma has the advantageous effect of passivating (both chemically and electronically) the surface of thesource substrate.

According to a preferred embodiment, the method can further comprise a step of providing a predetermined splitting area inside the source substrate before or after the local treatment step. Preferably, this step includes implanting an atomicspecies into the source substrate to form a zone of weakness at which splitting is intended to occur.

The inventive method can further comprise a further step of providing a dielectric layer, in particular an oxide, on the source substrate before or after the implanting step. In case the predetermined splitting area is provided after providingthe dielectric layer, the dielectric layer could be at least partially removed to improve surface quality. In all other cases, the dielectric layer is used to provide the desired dielectric properties of the buried layer of the GeOI substrate over thepassivated and non passivated regions of the source substrate. The local passivation treatment may create a slight surface topology. Providing the dielectric layer on the locally passivated surface has the advantage that a planarization step (e.g., byCMP) can be carried out. This will also form a surface which can easily be bonded to other substrates.

In a further preferred variant, the locally passivated source substrate can be annealed to stabilize the GeO.sub.xN.sub.y passivation surface, in particular for 1 hour or more at about 600.degree. C. This can be performed before or after themask removal. The thermal treatment has the consequence of stabilising the GeO.sub.xN.sub.y regions and, depending on the mask type used, also to sublime the mask layer.

A further method comprises attaching, preferably by bonding, of the source substrate to a handle substrate, and then detaching the source substrate at the predetermined splitting area, to thereby obtain the locally passivated GeOI substrate. With the stable GeO.sub.xN.sub.y dielectric layer on the source substrate it becomes possible to transfer a thin Ge layer together with the GeO.sub.xN.sub.y layer in the nitridized regions to achieve the desired locally passivated GeOI substrate. Thehandle substrate is preferably a silicon wafer.

Advantageously, the method can further comprise a step of providing a dielectric layer, in particular an oxide, on the handle substrate before the substrates are bonded together, in particular when there is no dielectric provided on the sourcesubstrate. In the case of a silicon wafer, the dielectric can be a thermal oxide and/or a deposited oxide. Thus, bonding can be achieved between the locally passivated surface of the source substrate and the dielectric of the handle substrate, betweenthe dielectric of the source substrate and the surface of the handle substrate without dielectric, or between the dielectric layers of the source and handle substrate.

According to an advantageous variant, the method can furthermore comprise a step of activating the handle substrate using a plasma, in particular an oxygen plasma and/or NH.sub.3, N.sub.2 or N.sub.2O plasma, in particular mixed with Ar, beforethe bonding step. Activating of the handle substrate surface provides improved bonding between the substrates.

Preferably, bonding can be carried out directly after the plasma treatment step is conducted on the source substrate or the handle substrate without any intervening further process step. By immediately carrying out the bonding step, adeterioration of the GeO.sub.xN.sub.y surface can be prevented and superior final products be achieved. Thus, according to the invention, passivation of the Ge material and activating of the surface for bonding are achieved in a single step. Of course,prior to bonding, the patterned mask needs to be removed.

Advantageously, the mask used in the mask providing step can be at least one of a shadow mask, in particular a Teflon mask or metal mask or a deposited mask, in particular a photo resist based mask, with a thickness of 1 .mu.m or less or agermanium oxide or GeO.sub.2 mask. It was found that these types of masks are suitable to provide the desired locally passivated regions in the source substrate. Prior to bonding, the mask is removed using, for example, dry or wet etching, inparticular a plasma etching using N.sub.2, or by a thermal treatment as long as the passivation is not negatively affected.

Preferably the local treatment step can comprise the steps of: providing a germanium oxide or GeO.sub.x layer, which can be the natural or a deposited one, on the source substrate, providing a photo resist layer, nano-imprinting the photo resistlayer, and providing the pattern by plasma etching in particular reactive ion etching (RIE). According to an alternative embodiment, the GeO.sub.x layer can also be patterned using a laser or electron beam treatment. Using the nano-imprinting step,locally passivated structures like islands of a micro- and/or nanometric size are readily achievable.

Advantageously, the photoresist layer can be removed before the local passivation such that the step of removing the photoresist layer does not have an impact on the locally passivated regions.

According to a preferred embodiment, the method can furthermore comprise a step of providing alignment marks on or in the source substrate. According to the invention, the substrate will present areas of the Ge "top" layer that should receiven-MOS type of devices due to improved electron mobility over the locally passivated regions and other areas away from the locally passivated regions are suited to receive p-MOS type of devices as; in those regions; the hole mobility is better. Thealignment marks will support the steps of manufacturing the n-MOS and/or p-MOS devices as they provide a reference point so that the various devices can be formed on their corresponding regions.

Advantageously, the method can further comprise a step of providing recesses in the source substrate pattern. The pattern of the recesses is chosen such that it becomes possible to know where the buried locally passivated regions arepositioned. It is not necessary to use the same pattern as the one of the passivated regions as long as positioning of preferably all buried locally passivated regions is possible.

According to a further preferred embodiment, a dielectric, in particular a SiO.sub.2 layer, can be provided in the recesses. After depositing the SiO.sub.2 layer, a planarization step, e.g., a CMP step, can be carried out to obtain a surfacewith SiO.sub.2 islands inside a Ge surface. Based on the properties of the dielectric, it becomes possible to identify the passivated regions. Preferably, this dielectric layer is the same as the one described previously.

Preferably the dielectric layer can be provided such that the predetermined splitting area is crossing the recesses of the source substrate. This has the advantage that the dielectric is visible on the surface thus the locally passivatedregions buried in the substrate can be identified from outside the substrate. Preferably, the recesses can have a depth of 0.5 to 2 .mu.m.

The means for alignment can be provided before or after providing the locally passivated regions. Providing them before the passivated regions has the advantage that the fabrication process concerning the means for alignment does not have animpact on the locally passivated regions.

The invention also relates to a germanium-on-insulator substrate comprising locally passivated regions, in particular, substrates obtainable according to one or a combination of any of the methods described herein. With such agermanium-on-insulator substrate, the above described advantages can be achieved.

Thus, the invention relates to a germanium-on-insulator substrate (GeOI) comprising buried passivated regions. According to a preferred embodiment, the germanium-on-insulator substrate can furthermore comprise alignment marks, in particularSiO.sub.2 islands, configured and arranged to identify the positions of the buried passivated regions. Preferably the alignment marks, extend up to the surface of the GeOI substrate.

Another embodiment of the invention is an electronic device comprising nmos and pmos device structures on or in one of the germanium-on-insulator substrates described herein, wherein the nmos structures are provided over the localised,passivated regions, and the pmos structures are provided over other regions of the germanium-on-insulator substrate. Other electronic devices incorporating the novel substrates of the invention can be envsisioned by those persons of ordinary skill inthe art. The substrates that include alignment marks are especially useful in forming these electronic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous and preferred embodiments of the invention will be described in the following text by referring to the drawing figures, wherein:

FIGS. 1A-1G show a first embodiment of the method for fabricating a germanium-on-insulator type wafer according to the invention,

FIGS. 2A-2G show a second embodiment of the method for fabricating a germanium-on-insulator type wafer according to the invention,

FIGS. 3A-3G show a third embodiment of the method for fabricating a germanium-on-insulator type wafer according to the invention,

FIGS. 4A-4F show a fourth embodiment of the method for fabricating a germanium-on-insulator type wafer according to the invention, and

FIG. 5 illustrates a fifth embodiment of the invention, namely an electronic device comprising n-MOS and p-MOS structures provided on a substrate fabricated a germanium-on-insulator type wafer according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following specification, the overall method for fabricating a germanium-on-insulator type wafer according to the invention will be described based on the well known SmartCut.TM. technology. However, other suitable semiconductor oninsulator providing manufacturing methods can also be adapted to the invention, for example, a bonding and grind/etch back process.

FIG. 1A illustrates a germanium (Ge) substrate 1 or, as a variant, a substrate with a germanium containing layer, in particular an epitaxial Ge layer or a silicon and germanium comprising layer SiGe, provided on one of its main surfaces. In thecase of a SiGe layer, the Ge content is preferably at least 50%, more preferred more than 70%. Prior to further treatment steps, the surface 3 of the source substrate 1 may be cleaned using, for instance, a HF base solution (fluoric acid).

FIG. 1B illustrates a handle substrate 5 which can be, for example, a germanium wafer, a silicon wafer, a silicon carbide wafer, a wafer presenting a silicon germanium front surface or a gallium arsenide wafer. Eventually, also a quartz typewafer could be used. Both the source substrate 1, as well as the handle substrate 5, may have any suitable size of form such as, for example 200 mm or 300 mm type wafers.

FIG. 1C illustrates steps b) and c) of the inventive method for fabricating a locally passivated germanium-on-insulator wafer according to claim 1 which consists of first providing a patterned mask 7 over the source substrate 1 and then treatingthe source substrate 1 via the patterned mask 7 to obtain locally GeO.sub.xN.sub.y regions 9 in or on the source substrate 1.

The mask can be a contact mask, thus provided on the source substrate 1. According to a variant, as illustrated in FIG. 1C, a non-contact mask positioned above the surface 3 of the source substrate 1 can be provided. In this case, the mask 7can be a Teflon mask or a metal on the source substrate 1.

The openings 11 in the mask 7 are of micrometric or nanometric size so that the locally passivated regions 9 of the source substrate 1 are also in the micrometric or nanometric range. They can have a regular size or varying size with respect toeach other.

According to this embodiment of the invention, the treatment step is a nitridizing step using a nitrogen comprising plasma, in particular a NH.sub.3, N.sub.2 or N.sub.2O plasma diluted in an Argon plasma, to incorporate nitrogen atoms intosubstrate 1.

Preferably, the plasma is applied for about 60 seconds at low pressures of less than 40 mTorr, in particular in a range of 1-10 mTorr. The preferred temperature range is 25.degree. C. up to 600.degree. C. Optimized results have been achievedin a pressure range of 5 mTorr and at temperatures of 150.degree. C. It appears that the lower the pressure of the plasma, the more nitrogen can be incorporated. The plasma treatment can be followed by a temperature treatment around 600.degree. C.This is particularly useful in the case where the mask 7 is formed of GeO.sub.2. The thermal treatment has then the consequence of stabilising the GeO.sub.xN.sub.y regions 9 and also to sublime (to render volatile) the GeO.sub.2 mask layer. Thistreatment is a surface treatment and the thickness of the N rich regions is less than 10 nm, preferably less than 5 nm, more preferably 3 nm.

Actually, due to the presence of oxygen as natural germanium oxide on the surface of the germanium substrate 1 or in the environment during the passivation treatment, the nitridizing steps leads to the creation of GeO.sub.xN.sub.y type islandsin those regions 9. In the final germanium-on-insulator substrate (see further down), the Ge material of the top layer above those islands shows a high electron mobility.

Following the removal of the mask 7, a predetermined splitting area 13 is provided inside the source substrate 1 as illustrated in FIG. 1D. The predetermined splitting area 11 is essentially parallel to the main surface 3, which is providedwith the locally passivated germanium oxynitride regions 9. According to the SmartCut.TM. technology, the predetermined splitting area is obtained by implanting atomic species 15, for instance hydrogen or helium ions, with a predetermined energy anddose into the source substrate 1. According to a variant, this step can also be carried out before the removal of the mask 7.

Afterwards, as illustrated in FIG. 1E, a dielectric layer 17, in particular an oxide layer such as a silicon dioxide layer, is provided, e.g., by deposition, on the source substrate 1. This layer 17 extends over the entire surface of the sourcesubstrate 1, thus also over the passivated regions 9. Subsequently, a planarization step could be carried out, e.g., by CMP.

In a subsequent step, the source substrate 1 with the nitridized regions 9 and the dielectric layers 17 is attached, in particular by bonding, to the handle substrate 5 to form a source-handle compound 19. Bonding occurs between the surface ofthe handle substrate 5 and the surface 21 of the dielectric layer 17 (see FIG. 1F).

FIG. 1G illustrates the result of the detachment step which occurs at the predetermined splitting area 13. Typically, a thermal annealing leads to the desired detachment, however other energy providing means may also be suitable in replacementor in complement of the anneal. Actually, during annealing, a weakening of the predetermined splitting area 13 until complete detachment between the remainder 23 and the newly formed germanium-on-insulator substrate 25 with locally passivated regions 9occurs. The inventive germanium-on-insulator substrate 25 with locally passivated regions 9, comprises the handle substrate 5, the dielectric layer 17, the passivated regions 9 and a transferred germanium layer 27. Like already mentioned, the substrate25 shows improved electron mobility in the passivated regions and in the non passivated regions the hole mobility is not negatively affected by the passivation.

The remainder 23 of the source substrate 1 can then be reused as a source substrate 1 in subsequent locally passivated germanium-on-insulator manufacturing processes.

According to variants of the first embodiment, the sequence of the various steps can be changed. Thus, according to one variant, the ion implanting step illustrated in FIG. 1D is carried out before creating the nitridized regions 9, thus beforethe step illustrated in FIG. 1C. Furthermore, according to a second variant, the dielectric layer 17 is provided on the nitridized regions 9 before ion implantation. Thus, the step illustrated in FIG. 1E can be carried out before the step illustratedin FIG. 1D. Eventually, in this variant, a surface region of the dielectric layer 17 is removed after ion implantation to improve the surface quality. According to a third variant of the first embodiment, prior to applying the nitrogen containingplasma, an oxygen and/or argon containing plasma can be applied to improve and/or thicken the germanium oxide layer which is already present on top of the source substrate 1. The role of the nitrogen containing plasma is then to activate the surface ofthe source substrate 1 in the nitridized regions 9.

The final product 25 can furthermore receive additional treatments, such as a polish and/or a heat treatment, to stabilize the structure.

FIGS. 2A-2G illustrate a second embodiment of the inventive method.

The steps illustrated in FIGS. 2A-2D correspond to the steps illustrated in FIGS. 1A-1D. Their description is therefore not repeated again, but incorporated herewith by reference to the description of FIGS. 1A-1D. The difference between thefirst and second embodiments is that, instead of providing a dielectric layer 17 onto the source substrate 1 following the nitridizing step, a dielectric layer 31, e.g., silicon dioxide, is provided, for example by deposition or a thermal treatment, onthe handle substrate 5, like illustrated in FIG. 2E.

The surface 33 of the dielectric layer 31 undergoes an activation using a plasma, in particular an oxygen plasma and/or nitrogen containing plasma e.g., NH.sub.3, N.sub.2 or N.sub.2O plasma. The plasma treatment of layer 31 is carried out underconditions compared to the plasma treatment conditions of the source substrate described in detail with respect to FIG. 1C.

FIG. 2F then illustrates the step of attaching, in particular by molecular bonding, the source substrate 1 to the handle substrate 5 to form the source-handle compound structure 33, In this case, bonding occurs at surface 33 of the dielectriclayer 31 and the surface 3 of the source substrate 1 with the passivated regions 9.

Just like in the first embodiment, the next step, illustrated in FIG. 2G, consists in detaching the germanium-on-insulator type substrate 37 from the remainder of the source substrate 1 (not shown). The germanium-on-insulator substrate 37 inthis embodiment comprises the handle substrate 5, the dielectric layer 31, the locally passivated regions 9 and the transferred layer 27.

According to a variant, the steps illustrated in FIGS. 2C and 2D can be exchanged such that the passivated regions 9 are achieved after providing the predetermined splitting area 13. In this case, attachment can be carried out immediately afterthe plasma treatment on the source substrate 1 and the plasma treatment on the dielectric layer 31 and an improved stability of the stoichiometry of the GeO.sub.xN.sub.y regions 9 is observed.

Of course, the methods according to embodiment 1 and embodiment 2 can be combined in which case the attachment is achieved between dielectric layer 17 and dielectric layer 31.

FIGS. 3A-3G illustrate a third embodiment of providing a locally passivated germanium-on-insulator substrate according to the invention. FIGS. 3A-3G illustrate in detail one possibility to provide a patterned mask and, using this mask, to treatthe source substrate 1 to obtain locally passivated regions 9 on the source substrate 1. The mask in this embodiment is in contact with the surface 3 of the source substrate 1.

FIG. 3A corresponds to FIGS. 1A and 2A, thus represents the source substrate 1, a germanium wafer or a wafer with a germanium layer on its surface 3. FIG. 3B illustrates the next step of providing a germanium dioxide GeO.sub.2 layer 41 on thesurface 3 of the source substrate 1. The germanium dioxide layer 41 corresponds to the natural oxide layer or can be a deposited one.

The next step consists in providing a photoresist layer 43 on the germanium dioxide layer 41. Subsequently, using a nano-imprint process known in the art, the photoresist layer 43 is patterned. Via the patterned photoresist layer 45, apatterned mask 47 is created inside the germanium dioxide layer 43 to play the role of mask 7, as illustrated in FIG. 1C. Patterning of layer 43 is e.g., achieved by using a reactive ion etching process. As an alternative, instead of providing thephotoresist layer, also a laser ablation, ion beam or electron beam sputtering process can be used to create the mask 47 in the germanium dioxide layer 41. Preferably, the photoresist layer 45 is removed before the passivation step such that the step ofremoving the photoresist layer does not have an impact (removal) on the passivated surface layer. Via the mask 47, a nitridizing treatment, as described with respect to FIG. 1C, is then applied to form the nitridized regions 9 in the source substrate 1. The result of this step is illustrated in FIG. 3F.

Finally, the mask 47 is removed, e.g., using an N.sub.2 plasma or a thermal treatment at about 600.degree. C. for one hour or more.

FIGS. 4A-4F illustrate a fourth embodiment for fabricating a locally passivated germanium-on-insulator substrate according to the invention. As already illustrated in FIGS. 1A, 2A and 3A, the step illustrated in FIG. 4A consists in providing agermanium substrate 1 or a substrate comprising an epitaxial germanium layer, such that the surface 3 of substrate 1 is a germanium layer. Process steps already previously described are not repeated again in detail, but their description is incorporatedherewith by reference.

Subsequently, using a mask 51, recesses 53 are provided in the source substrate 1. These recesses 53 have a depth d.sub.1 and are, for example, obtained using an etching process such as reactive ion etching. The recesses 53 have a micrometricdepth of, for example, 1 micron (see FIG. 4B).

Subsequently, the process step as illustrated in FIG. 1C is carried out (FIG. 4C), namely the source substrate 1 with the recesses 53 is treated via mask 7 to obtain locally passivated regions 55 comparable to the ones 9 illustrated in FIG. 1C. Actually, the only difference between the locally passivated regions 55 and the ones 9 illustrated in FIG. 1C is that, now, these locally passivated regions 55 are provided inside the recesses 53.

As a next step (FIG. 4D), a dielectric layer 57, e.g., SiO.sub.2, is provided over the source substrate 1 which covers the locally passivated regions 55 and the recesses 53. To smoothen the surface of the dielectric layer 57, a polishing step,such as CMP, is carried out.

Then, as illustrated in FIGS. 1D and 4E, a predetermined splitting area 13 is created inside the source substrate 1. According to the invention, the predetermined splitting area 13 is created at a depth d.sub.2 being smaller than the distanced.sub.1 of the surface of the germanium substrate down to the bottom 59 of the recess 53.

Subsequently, the source substrate 1 with dielectric layer 57 is attached, preferably by bonding, to a handle substrate 5 (like described with respect to FIGS. 1B and 1F) and detachment occurs at the predetermined splitting area 13 asillustrated in FIG. 1G. After detachment, the locally passivated germanium-on-insulator substrate 61, as illustrated in FIG. 4F, is obtained. As the alignment marks 63 are on the surface of substrate 61, it becomes easy to identify the position of thegermanium islands 65 overlaying the locally passivated regions 55 based on the fixed positional relationship between alignment marks 63 and passivated regions (based on their respective masks 7 and 51).

Embodiments 1-4 can be freely combined to achieve further variants of the invention.

The locally passivated germanium-on-insulator substrates 25, 37 and 61, as well as the various variants thereof, find their application in devices having n-MOS and p-MOS structures fabricated on a single substrate. In particular, advantage istaken of the high electron mobility in the passivated regions and the good hole mobility in the other regions.

FIG. 5 illustrates the substrate 61 and further electronic structures. As illustrated in FIG. 5, n-MOS devices 71, 73 are positioned above the passivated regions 55 (because of higher electron mobility in this area) and p-MOS devices 75, 77 arefabricated over the non passivated areas (because of higher hole mobility). This allows to have a wafer on which both type of devices can have improved performance. The alignment marks 63 on the surface are advantageously used to precisely positioneach respective device 71, 73, 75, 77 over the specific area of the substrate 61. Thus superior devices based on germanium-on-insulator substrates can be fabricated.

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Fluorine-free fused ring heteroaromatic photoacid generators and resist compositions containing the same
Method and apparatus for reducing power consumption used in communication system having time slots
High power fiber amplifier with stable output
Light-emitting device
Exposure method, exposure apparatus, and method for producing device
Light-emitting device with a spacer at bottom surface
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Resistance exercise apparatus
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Cellular phone
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Saddle mattress
Device to replace the rolls in a four-high rolling stand for sheet and/or wide plate
Portable blower
Distinguishing between dopant and line width variation components